Melt the chocolate drops in a heatproof bowl set over a pan of gently simmering water, stirring occasionally.
Put the flour, baking powder, caster sugar, cocoa powder, milk and egg in a food processor or mixer and blend for 1 minute at low speed.

Add the melted chocolate and blend for 1 minute at high speed. Fold in the hazelnuts.

Lightly grease four 175ml pudding basins or dariole moulds with butter. Spoon the chocolate mixture into the basins and cover each one with a piece of greaseproof paper and foil, then secure with string.

Place the puddings on a rack set in the bottom of a large saucepan. Pour enough just-boiled water into the pan to come three-quarters of the way up the sides of the basins.

Cover the pan with a tight-fitting lid and simmer over a medium-low heat for 1 hour, topping up with more water if necessary, or until a skewer inserted into the centre of a pudding comes out clean. Carefully remove the puddings from the pan and allow to cool for 10 minutes.

Turn out the puddings onto serving plates. Pour the Chocolate Hazelnut Spread over the puddings and serve.